to provide a therapeutic range of a drug to an individual patient- concentrations that result in maximum benefit with least side effect
Drugs act by...(4)
replacing or acting as substitutes for missing chemicals
increasing or stimulating certain cellular activities albuterol B2
depressing or slowing cellular activities atenolol B1
interfering with the function of foreign cells (chemotherapeutic)
drugs achieve their effects by
opening or closing ion channels, activating biochemical messengers, inhibiting cellular processes, turning on a cellular function.
Receptors are most likely proteins or nucleic acids on cell wall or in cytoplasm that regulate normal cell function. Drugs interact with receptors (binding) to produce a response.
possible actions at receptor site
Agonist: stimulates at receptor ex albuterol
Antagonist: blocks at receptor ex atenolol
Drug Enzyme Interactions
effect of meds alter the others; does this with liver; certain enzymes process drugs; some people cant process drugs because they don’t produce the proper enzymes
meds attack certain cells, such as rapidly reproducing cancer cells. Usually never happens, almost always attacks healthy cells as well.
way the body processes drugs and includes absorption, distribution, metabolism (biotransformation), and excretion.
the amount of drug needed to have a therapeutic effect
extra amount of medicine initially to kick start into the critical concentration
Absorption, Distribution, Metabolism, and Excretion. Working together to achieve critical concentration.
drug moves from site of administration into venous or lymphatic circulation. Affected by dosage form and route of administration and patient characteristics. Drug transported by vascular system to site of activity. Can stay in blood stream and be reversibly bound to protein or circulate unbound.
Bioavalability describes how much of what is administered makes it into circulation to produce effects.
processes involved in absorption
include passive diffusion (most important), active transport (carriers that form complex with drug and carry through membrane and then dissociate), filtration (through pores- very small)
pros and cons
Pros:easy, self administration, cheap
Cons: takes long time, GI issues/irritation, self administration issues, choking
pros and cons
Pros: Most rapid route of absorption aside from IV
Pros: fastest route, more effective in reaching tissue, accuracy
Cons: difficult to administer/ keep/ maintain, painful, complications, expensive
pros and cons
Pro: localized affect
Cons: Incorrect technique, secondary infection,
pros and cons
Pro: easy, lower side effects, generally inexpensive, self administered, long lasting
Cons: allergy, improper use/ understanding
pros and cons
Pros: fast absorption, good for certain populations ie. Children
Cons: uncomfortable, technique,
absorption is affected by
nature of absorbing surface, blood flow to site, solubility of drug, ph and affect of ionization (more highly ionized less absorbable), drug concentration, dosage form
drug movement from bloodstream to the site of action and to storage sites. Move first into those organs with rich blood supply (heart, liver, kidney, brain) then into muscle and fat
factors that affect distribution
2. tissue perfusion
3. how the drug is formulated
most drugs bound to proteins in the blood to be carried in circulation, can’t diffuse into capillaries due to size. Drugs are variably bonded and can be released slowly or quickly which affects onset of action. Drugs that are bound to protein are inactive. As dissociate- free drug becomes active. So another drug can cause loss of protein binding or low protein levels may result in more toxicity.
In tissue, a drug may bind to receptors and achieve affect or to a _________ receptor with no effect, or can be ___________ and eliminated
(Biotransformation): conversion of compounds to less toxic or nontoxic substances and prepare for excretionLiver
First pass effect
from gastric absorption, po meds go to portal venous system into liver where transformed by enzymes, so increased doses needed as compared to parenteral where some of dose reaches reactive tissue before going to liver
Hepatic enzyme system
most important site “hepatic microsomal system” . besides metabolizing drugs and preparing them for excretion, may actually convert an active prodrug to an active compound.
Phase I - Alters drug to more polar and water soluble form to aid excretion. Involves cytochrome P450 system in liver.
Phase II is conjugation of compound to inactivate and then eliminate. (union of polar group of drug with another substance in body)
Enzyme induction occurs when one compound increases the activity of the enzyme system. This increased enzyme activity hastens the breakdown of other drugs that use the same pathway.
Genetics also a fact as certain subsets of a major cytochrome system P450 may be absent or diminished in some population
removal of drug or its metabolites from the body
kidneys play the major role with passive glomerular filtration, and active tubular secretion, or partial reabsorption
occurs through skin, saliva, lungs, bile (from liver to bile to duodenum to feces), feces
acidity of urine may affect excretion KIDNEY
the amount of time it takes to go from peak drug to half the concentration of the drugExample 500 mg->250 mg-> 125mg…
It takes 3-5 doses to achieve a steady state
Serum drug concentration
The amount of a drug or other compound in the circulation, both bound to proteins and unbound, the latter of which generally corresponds to the theraepeutically active fraction
decreased response to drug- may be due to more rapid metabolism, fewer receptors
needs drug to have normal function (can be physical psychological)
symptoms resulting from decrease in drug in dependent individual
tolerance to different drug due to chemical similarities
Factors influencing drug effects
1. Weight- Most medicines when tested are tested on 140-170 lb males
4. Physiological factors- things that are occurring with that individual at the time of administration ex. hydration